Added Kosovo

Right now Kosovo doesn't have its own official iso3166 standart code, but it is assigned temp xk/xkx codes.
Codes are temporary till Kosovo is assigned its own country codes.
Also there is no numeric country code (even temp/unofficial), so used phone code just to make code compiled.

Code was formatted with cargo fmt, to get verbose representation of relevant changes see this commit

Used data from:

• https://en.wikipedia.org/wiki/Kosovo
• https://en.wikipedia.org/wiki/.xk

Codes:

• alpha2 - XK
• alpha3 - XKX
• numeric - 383 (### Used phone code because numeric id was not assigned, so the country doesn't still has it, added just to make code compile ###)
• full name - Kosovo